The site contains a number of short articles, with numerous pictures, of various gun related experiments and tests (front page and Original Chapters page), as well as educational material (The Education Zone).
As examples of some of the things covered, there are articles on the stopping power (vs a variety of different caliber guns and rifles) of various barriers (interior walls, bulletproof glass, car doors, body armor, etc.); the effects of different kinds of bullets; cheap vs good, damaged, breaching rounds, rock salt, etc., with estimates of penetrating power on a human. The educational page has things such as how to clear a doublefeed malfunction, how to use corrosive ammo, a day with snipers, introductions to various types of guns, how to clean different guns and rifles, etc.
Lots of good information, and plenty of large photos (about 8" x 5" on my screen) so you can see exactly what he's talking about!